The present invention relates to a cooling medium temperature monitoring system for monitoring the temperature of cooling medium in the outlet of a cooling medium passage provided in a stator coil of a rotary electric machine.
According to conventional system of this type, there is a cooling medium temperature monitor of a turbine generator as shown in FIGS. 1, 2 and 3. FIG. 1 is an explanatory view showing the air flowing within a turbine generator; FIG. 2 is a sectional view showing a stator coil, and FIG. 3 is an explanatory view of a monitoring circuit of the temperature of cooling medium in the outlet of the cooling medium passage of the stator coil.
In FIG. 1, reference numeral 1 designates a frame of a generator, which is constructed as an airtight structure to seal hydrogen gas therein. Numeral 2 designates a stator core; numeral 3 designates a stator coil; numeral 4 designates a rotor; numeral 5 designates bearings for supporting both ends of a rotational shaft 4a of the rotor 4; numeral 6 designates a blower projected from the outer periphery of one end of the rotor 4; and numeral 7 designates a hydrogen gas cooler. Reference character G.sub.1 designates an arrow showing the direction of the low temperature hydrogen gas flow; character G.sub.2 designates an arrow showing the direction of the hydrogen gas flow in the stator coil 3; character G.sub.3 designates an arrow showing the direction of the hydrogen gas flow in the outlet of a cooling medium passage provided in the stator coil 3; and character G.sub.4 designates an arrow showing the direction of the hydrogen gas flow in the rotor coil.
The cooling operation of the hydrogen gas is described as follows. The hydrogen gas is sealed in the frame 1, and fed to the gas cooler 7 by the blower 7 provided on the rotor 4 and is cooled. The cooled low temperature hydrogen gas 8 flows in the direction of the arrow G.sub.1. The hydrogen gas 8 then flows from the gas inlet of the stator coil 3 axially through the stator coil 3 (in the direction of the arrow G.sub.2). The hydrogen gas removes the generated heat such as resistance losses of the stator coil 3 at this time, and is exhausted from the outlet of the cooling medium passage of the stator coil 3 in the direction of the arrow G.sub.3.
On the other hand, the low temperature hydrogen gas fed to the rotor coil of the rotor 4 flows from both ends of the rotor coil toward the center in the axial direction (of the arrow G.sub.4). Then, the hydrogen gas removes the heat generated in the rotor coil and is exhausted from the center of the rotor coil.
The exhausted hydrogen gas which is at a high temperature is fed by the blower 6 to the gas cooler 7. Then, the heat from the hydrogen gas is thermally exhanged to the cooling water so that the gas again becomes a low temperature gas, and is again circulated in the directions of the arrows G.sub.1, G.sub.2, G.sub.3 and G.sub.4.
The structure of the vicinity of the stator coil 3 is formed as shown in FIG. 2. In FIG. 2, reference numeral 12 designates a stator core; numeral 13 designates a stator slot, and the stator coil 3 is inserted into the slot 13. Numeral 14 designates a ground insulating member of the stator coil 3; numeral 15 designates a stator coil conductor; and numeral 16 designates a wind conduit buried in the conductor 15. The conduit 16 is provided over the entire length of the stator coil, the hydrogen gas is passed through the conduit 15 to thereby cool the stator coil 3. The stator coil 3 is interposed between spacers 18 and 19 and held so as not to be exhausted into the stator slot 13 by a slot wedge 20.
The monitoring circuit of the temperature of the cooling medium is shown in FIG. 3. The hydrogen gas removes the heat of the stator coil 3 when passing the stator coil 3, and is exhausted from the outlet of the cooling medium passage and hence the outlet of the conduit 16 (FIG. 2). Numeral 21 designates a plurality of temperature measuring elements provided in the outlet of the cooling medium passage of the stator coil 3 for measuring the temmperature of the hydrogen gas exhausted from the outlet. A temperature signal from the element 21 is inputted to a recording meter 22 and a warning unit 23.
The warning unit 23 always simultaneously monitors the temperature signals from all the temperature measuring elements 21, and generates an alarm when the temperature detected by any of the temperature measuring elements 21 exceeds a preset warning value. The warning value is determined to be a predetermined value depending only upon the temperature measuring data irrespective of the magnitude of the load of the generator and hence the amplitude of the armature current.
FIG. 4 shows a graph showing the relationship between the armature current, the temperature of the cooling medium in the outlet of the cooling medium passage and the warning value, where the rise of the temperature of the cooling medium with respect to the rated armature current is represented by 1 (p.u.).
Since the conventional cooling medium temperature monitor is constructed as described above, it is difficult to discover malfunctions of the stator coil until one of the temperature signals detected by the plurality of temperature measuring elements of the stator coil 3 exceeds the warning value to generate an alarm. Thus, the conventional cooling medium temperature monitor has a problem in that it takes a relatively long time after the malfunction occurs before the malfunction can be detected (i.e.--the time required for the stator to heat up).
Moreover, as can be seen from FIGS. 3 and 4, the temperature of the cooling medium (i.e.--hydrogen gas) in the outlet of the cooling medium passage, indicated by arrow G.sub.3, of the stator coil is directly proportional to the amplitude of the armature current. However, in the prior art monitoring system, the warning value is constant irrespective of the armature current. Therefore, the conventional monitor has a further problem in that a difference in warning values are inherent in prior art systems. Namely, since the prior art system generates an alarm only as a function of the output of the temperature measuring elements 21 (i.e.--irrespective of the magnitude of the armature current of the generator), which represents a preset warning value, the temperatures corresponding to small armature currents are lower than the temperatures corresponding to large armature currents so that malfunctions of the stator coil are difficult to correctly determine for low armature currents, while, on the other hand, alarms tend to be erroneously generated due to the rise of the temperature of the cooling medium in the area that the armature current is large.
In addition, in order to discover a malfunction of the stator coil 3 before generating an alarm, the variation in the armature current and the timing change of all of the temperature values indicated on the temperature recording meter are heretofore compared and judged by an operator. Therfore, operator's fatigue due to the constant monitoring becomes high, and the determination of whether or not the stator coil 3 is malfunctioning is performed based on the operator's experience, thereby resulting in an erroneous determination.